Uncovering regulatory mechanisms of salicylic acid (SA) biosynthesis in plants

Salicylic acid (SA) is a crucial defense molecule synthesized by plants that induces innate immune responses against biotic stresses. SA biosynthesis occurs via two pathways, the isochorismate synthase 1 (ICS1) pathway and the phenylalanine ammonia-lyase (PAL) pathway, and its regulation varies across different plant species. In Arabidopsis, the transcription factor CCA1 HIKING EXPEDITION (CHE) plays a key role in regulating ICS1 and SA biosynthesis in the systemic tissue to establish systemic acquired resistance (SAR), which is a broad spectrum of resistance plants obtain in uninfected tissue. However, the mechanisms that regulate SA biosynthesis and SAR establishment in other plant species remain largely unexplored. To address this knowledge gap, we investigated the regulation of SA biosynthesis in three plant species, Arabidopsis thaliana, Camelina sativa, and Brassica napus. We especially focused on analyzing the binding of CHE to the ICS1 promoter region in the selected plant species. We discovered that while Camelina sativa has the same CHE binding site as Arabidopsis, the other plant species such as B. napus has a G to A substitution of first base pair in the CHE binding site, resulting in no binding of BnCHE to BnICS1. These findings suggest that the regulation of SA biosynthesis and SAR establishment in B. napus and other plant species varies as compared to Arabidopsis and C. sativa Our study sheds light on the variation of SA-related defense strategies in plants and may lead to new approaches to enhancing plant immunity against various pathogens.